Optical device, optical semiconductor device, and optical information processor comprising them

ABSTRACT

An optical semiconductor device is provided that includes an emitted beam dividing portion ( 61 ) for dividing an emitted light beam from the laser element ( 51 ), a reflected beam dividing portion ( 71 ) for dividing a reflected light beam from an information recording medium ( 3 ) into light beams in different focused states, servo-signal-detecting photodetector elements ( 43, 45 ) for receiving the reflected light beams obtained by the division by the reflected beam dividing portion in a defocused state, a first diffraction grating that is provided in the emitted beam dividing portion and that diffracts the reflected light beam having passed through the reflected beam dividing portion, and a signal-detecting photodetector element ( 47 ) for receiving reflected light beams having been subjected to the diffraction by the first diffraction grating.

TECHNICAL FIELD

[0001] The present invention relates generally to an optical informationprocessing device that performs the recording, reproduction, erasure,etc. of information with respect to an information recording medium suchas an optical disk. The present invention particularly relates to anoptical semiconductor device employed in an optical head device, whichhas a function of detecting reproduction signals and various kinds ofservo signals, and to an optical element used therein.

BACKGROUND ART

[0002] The following description will depict a configuration andprinciple of operation of a conventional optical semiconductor deviceused in an optical information processing device, which has a functionof detecting reproduction signals and various kinds of servo signals,while referring to FIG. 10. A light beam emitted from a semiconductorlaser element 101 as a light source is diffracted in a Y direction asviewed in the figure by a three-beam-generating diffraction gratingelement 102, so that a zeroth order light of the same becomes a mainbeam while the first order lights (±1) become sub beams. These threebeams obtained by division are focused on an information recordingmedium 106 by an objective lens 105 and reflected by the informationrecording medium 106, and then enter a hologram element 103.

[0003] The hologram element 103 is a diffraction grating composed ofgratings, each in a curved line form. A reflected light beam from theinformation recording medium 106 is divided by the hologram element 103,where the +1-order diffracted light 107A is subjected to a convergingeffect, while the −1-order diffracted light 107B is subjected to adiverging effect, and they are guided to photodetector elements 104A and104B, respectively. The +1-order diffracted light 107A incident on thephotodetector element 104A is focused before a light-receiving surfacethereof, whereas the −1-order diffracted light 107B incident on thephotodetector element 104B is focused behind a light-receiving surfacethereof.

[0004] Reproduction signals and focus error signals are detected from amain beam among the reflected light beams having been guided to thephotodetector elements 104A and 104B, while tracking error signals aredetected from sub beams among the same. Focus servo is performed so thatthe +1-order diffracted light 107A and the −1-order diffracted light107B resulting from the division by the hologram element 103 have lightspots of substantially the same size on the photodetector elements.Tracking servo is performed so that sub beams have equal quantities oflight. The position of the objective lens is controlled by those servos,whereby an appropriate action of the optical semiconductor device as anoptical information processing device can be achieved.

[0005] In the foregoing conventional optical semiconductor device, thesame photodetector elements 104A and 104B are used for detectingreproduction signals and focus error signals. Since the +1-orderdiffracted light having been subjected to the converging and divergingeffects, respectively, at the hologram element 103 have to be receivedin a defocused state by the photodetector elements 104A and 104B, thephotodetector elements 104A and 104B must have large light-receivingareas, approximately 30000 μm² each. In the case where the photodetectorelements have large light-receiving areas, electric capacitancesassociated with the photodetector elements increase, thereby impairingthe quick responsiveness significantly. This particularly has been asignificant problem when CD-ROMs, DVD-ROMs, etc. are reproduced at ahigh speed, for instance, at several tens of times the normal speed.Furthermore, there has been the following problem as well: in the casewhere the photodetector element for detecting reproduction signals has alarge light-receiving area, stray light components incident thereon(external light, unnecessary reflection) increase, thereby decreasingthe signal-to-noise ratio (hereinafter referred to as S/N ratio) of thereproduction signals.

DISCLOSURE OF THE INVENTION

[0006] Therefore, with the foregoing in mind, it is an object of thepresent invention to solve the above-described problems of the priorart, and to provide an optical semiconductor device capable ofreproducing an information recording medium at a high speed andobtaining reproduction signals with an excellent S/N ratio, and anoptical information processing device employing the same.

[0007] An optical semiconductor device of the present inventionincludes: a laser element; an emitted beam dividing portion for dividingan emitted light beam from the laser element into a plurality of lightbeams; a reflected beam dividing portion for dividing a reflected lightbeam from an information recording medium into light beams in differentfocused states; servo-signal-detecting photodetector elements forreceiving the reflected light beams obtained by the division by thereflected beam dividing portion in a defocused state; a firstdiffraction grating that is provided in the emitted beam dividingportion and that diffracts the reflected light beam having passedthrough the reflected beam dividing portion; and a signal-detectingphotodetector element for receiving reflected light beams having beensubjected to the diffraction by the first diffraction grating.

[0008] This configuration allows the diffracted light obtained by thediffraction of the reflected light beam from the information recordingmedium by the first diffraction grating to substantially focus on thereproduction-signal-detecting photodetector element, thereby making itpossible to reduce a light receiving area of thereproduction-signal-detecting photodetector element. This allowsreduction of the capacitance associated with the photodetector element,thereby ensuring high-speed response of the reproduction signals.Furthermore, the reduction of the area of thereproduction-signal-detecting photodetector element leads to a decreasein stray light components incident on the detecting portion fordetecting reproduction signals, thereby allowing reproduction signalswith an excellent S/N ratio to be obtained.

[0009] An optical semiconductor device of the present invention that hasanother configuration includes: a laser element; a first optical elementthrough which an emitted light beam from the laser element passes; asecond optical element for dividing the reflected light beam from aninformation recording medium into light beams in different focusedstates; and a first diffraction grating that is provided in the firstoptical element and that diffracts the reflected light beam havingpassed through the second optical element.

[0010] An optical element of the present invention includes: a firstoptical element that is provided on one surface of a transparent memberand that includes first and second diffraction gratings; and a secondoptical element that is provided on the other surface of the transparentmember and that divides a reflected light beam into light beams indifferent focused states, wherein the first and second diffractiongratings are juxtaposed in a first direction, and gratings of the firstdiffraction grating are arranged in a direction different from the firstdirection.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a cross-sectional view illustrating a schematicconfiguration of an optical semiconductor device according to a firstembodiment of the present invention and an optical informationprocessing device employing the same.

[0012]FIG. 2 is a plan view of an emitted beam dividing portion in theoptical semiconductor device shown in FIG. 1.

[0013]FIG. 3 is an enlarged cross-sectional view specificallyillustrating a first diffraction grating in the emitted beam dividingportion shown in FIG. 2.

[0014]FIG. 4 is an enlarged cross-sectional view specificallyillustrating another embodiment of the first diffraction grating.

[0015]FIG. 5 is an enlarged plan view specifically illustrating anarrangement of detecting sections included in the photodetector elementin the optical semiconductor device shown in FIG. 1

[0016]FIG. 6 is a plan view illustrating an emitted beam dividingportion in an optical semiconductor device according to a secondembodiment of the present invention.

[0017]FIG. 7 is a plan view illustrating an emitted beam dividingportion in an optical semiconductor device according to a thirdembodiment of the present invention.

[0018]FIG. 8 is an enlarged plan view specifically illustrating anarrangement of detecting sections included in a photodetector element inthe optical semiconductor device according to the third embodiment ofthe present invention.

[0019]FIG. 9 is an enlarged plane view specifically illustrating anotherembodiment of an optical element in the optical semiconductor deviceaccording to the third embodiment of the present invention.

[0020]FIG. 10 is a cross-sectional view illustrating a conventionaloptical semiconductor device and an optical information processingdevice employing the same.

DESCRIPTION OF THE INVENTION

[0021] First Embodiment

[0022]FIG. 1 schematically illustrates an optical semiconductor device 1(basic cross-sectional configuration) according to the first embodimentof the present invention, and an optical information processing device 2in which the optical semiconductor device 1 is employed. The opticalinformation processing device 2 includes an optical semiconductor device1, an objective lens 4 for focusing a light beam emitted from theoptical semiconductor device 1 into an information recording medium 3(for instance, an optical disk, a magneto-optical disk, etc.), and amechanism controlling actions of the same (a servo mechanism, a signalprocessing circuit, etc., though not shown).

[0023] The optical semiconductor device 1 includes a semiconductorelement 11, a package 21 incorporating the same, and an optical element31 mounted on the package 21. By sealing the semiconductor element 11 inthe package 21 and the optical element 31, the optical semiconductordevice 1 has an integrated configuration. Increasing the effectivenessof the sealing improves the reliability of the semiconductor element 11.

[0024] The semiconductor element 11 includes a photodetector element 41having a plurality of detecting portions 43, 45, and 47 that areprovided by thermal diffusion or the like on a silicon substrate, and asemiconductor laser element 51 formed on the same silicon substrate. Thesemiconductor laser element 51 is made of a chemical compound providedat a bottom of a recessed part (not shown) having an inclined surface,formed in the silicon substrate by wet etching. The semiconductor laserelement 51 emits a laser beam with a wavelength of approximately 300 to800 nm. A light beam is emitted in a Y direction from the semiconductorlaser element 51, reflected by the inclined surface, so as to bedirected in a Z direction. It should be noted that such an inclinedsurface is unnecessary in the case where the semiconductor laser element51 is of a plane emission type.

[0025] Thus, by integrating the semiconductor laser element 51 and thephotodetector element 41 on one silicon substrate, it is possible toobtain a smaller-size optical semiconductor device. Furthermore, in thecase where the relative positional relationship between thesemiconductor laser element 51 and the photodetector element 41 isdetermined in the semiconductor process for processing the siliconsubstrate (for instance, by forming the detecting portions and therecessed part by using mask alignment), it is possible to reduce thenumber of steps, thereby shortening the time required for assembling andreducing the cost, as compared with a case where these elements areassembled separately and then they are fixed after their positionalrelationship is adjusted. Furthermore, the detecting portions and theintegrated circuit either for current-voltage conversion of electricsignals obtained from the detecting portions or for calculation of thesame may be provided integrally on a silicon substrate. This makes itpossible to further miniaturize the device. It should be noted that thelight source is not limited to the semiconductor laser, and a laser ofanother type (for instance, a laser in which SHG is used) may be used asa light source.

[0026] The optical element 31 is composed of a base made of a glass or aresin having substantial transparency with respect to a wavelength used,an emitted beam dividing portion 61 is provided on one of surfaces ofthe base, for dividing a light beam emitted from the semiconductor laserelement 51, and a reflected beam dividing portion 71 is provided on asurface opposite to the foregoing surface, for dividing a light beamreflected from the information recording medium 3. In the emitted beamdividing portion 61, a diffraction grating is provided that, asdescribed later, divides a light beam having passed through thereflected beam dividing portion 71 among the reflected light beam fromthe information recording medium 3. The emitted beam dividing portion 61and the reflected beam dividing portion 71 may be provided in the formof separated first and second optical elements. Furthermore, the emittedbeam dividing portion 61 may be configured simply to transmit the lightbeam emitted from the semiconductor laser 51, without having a functionto divide the emitted light beam from the semiconductor laser element51.

[0027] A light beam emitted from the semiconductor laser element 51passes through the emitted beam dividing portion 61 and the reflectedbeam dividing portion 71, and is focused on the information recordingmedium 3 by the objective lens 4. A reflected light beam from theinformation recording medium 3 is divided by diffraction in the Xdirection by the reflected beam dividing portion 71, and ±1-orderdiffracted light beams 83 and 85 thus obtained are guided to thedetecting portions 43 and 45 of the photodetector element 41.Furthermore, the O-order diffracted light (transmitted light) againenters the emitted beam dividing portion 61, and is diffracted by afirst diffraction grating provided on the emitted beam dividing portion61, so as to be guided to the detecting portion 47.

[0028] As shown in FIG. 2, the emitted beam dividing portion 61 includesregions serving as a first diffraction grating 63, a second diffractiongrating 65, and a third diffraction grating 67, thereby composing athree-beam-generating diffraction grating element. In the drawing,respective patterns of the diffraction gratings are illustrated with aplurality of lines. Furthermore, effective regions on the emitted beamdividing portion 61 corresponding to the beams to be collected into theobjective lens 4 are indicated as a main beam 81 (r representing aradius of the same), and sub beams 82 and 84.

[0029] The emitted light beam from the semiconductor laser element 51 isdiffracted by the emitted beam dividing portion 61 in a Y directionshown in the drawing. As a result of division, a O-order diffractedlight obtained from the first diffraction grating is obtained as themain beam 81, while ±1-order diffracted lights obtained from the secondand third diffraction gratings 65 and 67 are obtained as the sub beams82 and 84, respectively, thereby being collected into the objective lens4 as a focusing means.

[0030] On an optical axis extending between an emission point of thesemiconductor laser element 51 and a main beam spot incident on theinformation recording medium 3, let an air-equivalent distance from theemission point of the semiconductor laser element 51 to the emitted beamdividing portion 61 be represented by d. Here, the air-equivalentdistance means a value obtained by dividing a distance of lighttransmission through a medium by a refractive index of the medium.Further, let a numerical aperture of the objective lens 4 be representedby NA. Furthermore, let a distance in an X direction measured from apoint at which the optical axis and the emitted beam dividing portion 61cross on the emitted beam dividing portion 61 be represented by r. Here,the first diffraction grating 63 is formed so as to have an area thatincludes at least an area satisfying:

r≦d×tan(sin⁻¹(NA))  [Formula 1]

[0031] The reflected light dividing portion 71 is made of a hologramelement composed of gratings, each in a curved line form. Among thethree beams reflected from the information recording medium 3, as toeach of the main beam 81 and sub beams 82 and 84, the +1-orderdiffracted light beam 83 is subjected to a converging effect while the−1-order diffracted light beam 85 is subjected to a diverging effectwhen they are divided, and they are guided to the detecting portions 43and 45 of the photodetector element 41. On the other hand, the O-orderdiffracted light beam 87 of the main beam 81 of the reflected lightbeam, obtained by the division by the reflected beam dividing portion71, again enters the emitted beam dividing portion 61. This light beamis diffracted in the X direction by the first diffraction grating 63 ofthe emitted beam dividing portion 61. The first diffraction grating 63and the like are configured so that the +1-order diffracted light beam88 at the first diffracted grating 63 assumes a substantially focusedstate at the reproduction-signal-detecting detecting portion 47 providedon the photodetector element 41. This makes it possible to decrease thelight-receiving area of the reproduction-signal-detecting detectingportion 47, thereby allowing reproduction signals to be detected at ahigher speed. In examples, it was possible to set the light-receivingarea of the reproduction-signal-detecting detecting portion 47 to beapproximately 400 to 2500 μm².

[0032]FIG. 3 is an enlarged cross-sectional view specificallyillustrating the first diffraction grating 63 in the emitted beamdividing portion 61. In each diffraction grating in the firstdiffraction grating 63, gratings 63A in a step-like form are providedfurther. This configuration makes it possible to increase thediffraction efficiency of the +1-order diffracted light beam 88 incidenton the reproduction-signal-detecting detecting portion 47 with priorityto the diffraction efficiency of the −1-order diffracted light beam 89.Therefore, the quantity of the signal light incident on thereproduction-signal-detecting detecting portion 47 increases, therebyallowing reproduction signals with an excellent S/N ratio to beobtained. The step-like grating 63A can be formed by, for instance,carrying out photolithography and etching a plurality of times.

[0033]FIG. 4 is an enlarged cross-sectional view specificallyillustrating another configuration of the first diffraction grating 64.Gratings 64A, each having a triangular cross section, are provided asdiffraction gratings composing the first diffraction grating 64. It ispossible to directly form the triangular gratings 64A with an electronbeam (EB) whose intensity can be varied stepwise, or alternatively, itis possible to form the same by exposing and developing a photosensitivematerial and using the obtained photosensitive material as a die. Thisconfiguration also makes it possible to increase the diffractionefficiency of the +1-order diffracted light beam 88 incident on thereproduction-signal-detecting detecting portion 47 with priority to the−1-order diffracted light beam 89, thereby allowing reproduction signalswith an excellent S/N ratio to be obtained.

[0034] The first diffraction grating 63 may be composed of substantiallyrectangular diffraction gratings.

[0035]FIG. 5 is an enlarged plan view specifically illustrating thedetecting portions 43 and 45 and the reproduction-signal-detectingdetecting portion 47 of the optical element 41. The detecting portion 43includes three detecting sections 433, 435, and 437 extending in an Xdirection. The detecting section 433 is divided into three portions 433a, 433 b, and 433 c in a Y direction. The detecting portion 45, like thedetecting portion 43, includes the detecting sections 453, 455, and 457.The detecting section 453 is divided into three portions 453 a, 453 b,and 453 c in the Y direction. Focus error signals are detected from amain beam 81 among the reflected light beams having been guided to thedetecting portions 43 and 45, while tracking error signals are detectedfrom sub beams 82 and 84 among the same. Spots formed on the detectingsections are shown schematically in FIG. 5.

[0036] Here, let signal quantities detected at the detecting sections433 a, 433 b, 433 c, 435, 437, 453 a, 453 b, 453 c, 455, and 457 beexpressed as S(433 a), S(433 b), S(433 c), S(435), S(437), S(453 a),S(453 b), S(453 c), S(455), and S(457), respectively.

[0037] The focus servo is performed so that the spot on the detectingportion for the main beam has substantially the same size, that is, thefollowing is satisfied:

{S(433 a)+S(433 c)+S(453 b)}−{S(433 b)+S(453 a)+S(453 c)}=0

[0038] The tracking servo is performed so that the sub beams have equallight quantities, that is, the following is satisfied:

{S(435)+S(455)}−{S(437)+S(457)}=0

[0039] As described above, the 0-order diffracted light beam 87 from thereflected beam dividing portion 71 is incident on the first diffractiongrating 63 of the emitted beam dividing portion 61, and the +1-orderdiffracted light beam 88 obtained therefrom is incident in asubstantially focused state on the reproduction-signal-detectingdetecting portion 47. A spot formed by the +1-order diffracted lightbeam 88 on the reproduction-signal-detecting detecting portion 47 isshown schematically in FIG. 5. Since the +1-order diffracted light beam88 is incident thereon in the substantially focused state, thereproduction-signal-detecting detecting portion 47 may have a reducedarea for receiving light, as compared with the other detecting sections433, 435, and 437 for servo. The reduction of the light-receiving areaof the reproduction-signal-detecting detecting portion 47 allows thecapacitance associated with the photodetector element to be remarkablyreduced, thereby ensuring high-speed response of the reproductionsignals. Furthermore, this leads to a decrease in stray light componentsincident on the reproduction-signal-detecting detecting portion 47,thereby allowing reproduction signals with an excellent S/N ratio to beobtained.

[0040] Second Embodiment

[0041]FIG. 6 is a plan view illustrating an emitted beam dividingportion 62 according to the second embodiment. The present embodiment isan example of another embodiment of the emitted beam dividing portion 61used in the first embodiment.

[0042] The emitted beam dividing portion 62 is characterized in that afirst diffraction grating 68 is composed of gratings, each in a curvedline form. The other parts of the configuration are the same as those ofthe emitted beam dividing portion 61, and the same elements aredesignated with the same reference numerals. The configuration withgratings in the curved line form is able to apply a converging ordiverging effect to light beams when being diffracted by the firstdiffraction grating 68. Therefore, it is possible to change freely aposition of a focus of the reflected light beam from the informationrecording medium 3 by varying the curvature of the grating lines. Thismakes it possible to make the reflected light beam from the informationrecording medium 3 in a substantially focused state on thereproduction-signal-detecting detecting portion 47, irrespective of thedistance between the surface of the photodetector element and theemitted beam dividing portion 62.

[0043] The same effect as that of the first embodiment can be achievedby providing step-like gratings similar to those in the first embodimentin each grating of the first diffraction grating 68.

[0044] Third Embodiment

[0045] The third embodiment is an example in which the emitted beamdividing portion 61 in the first embodiment is modified so as to havestill another configuration. FIG. 7 is a plan view illustrating anemitted beam dividing portion 62A according to the present embodiment.FIG. 8 is an enlarged plan view specifically illustrating thephotodetector element. Elements other than a first diffraction grating69 and detecting portions 48 a, 48 b, 48 c, and 48 d for detectingreproduction signals have the same configurations as those of the firstembodiment, and they are designated with the same reference numerals.

[0046] In the emitted beam dividing portion 62A according to the presentembodiment, the first diffraction grating 69 is composed of a pluralityof diffraction grating regions with grating arrangement directionsdifferent from each other. In the first diffraction grating 69 shown inFIG. 7, four diffraction grating regions 69 a, 69 b, 69 c, and 69 d withthe grating arrangement directions different from each other areprovided so as to equally divide a spot of a reflected light beam fromthe information recording medium 3.

[0047] As shown in FIG. 8, a plurality of the detecting portions 48 a,48 b, 48 c, and 48 d are provided to receive light beams diffracted bythe diffraction grating regions 69 a, 69 b, 69 c, and 69 d. They arearranged so that light beams diffracted by the diffraction gratingregions 69 a, 69 b, 69 c, and 69 d substantially focus on the detectingportions 48 a, 48 b, 48 c, and 48 d for detecting reproduction signals,respectively.

[0048] With this configuration, the reflected light beam of the mainbeam 81 from the information recording medium 3 is diffracted by theplurality of diffraction grating regions 69 a, 69 b, 69 c, and 69 dcomposing the first diffraction grating 69, and is incident on thedetecting portions 48 a, 48 b, 48 c, and 48 d for detecting reproductionsignals, respectively. Thus, the use of signals detected by theplurality of detecting portions 48 a, 48 b, 48 c, and 48 d correspondingto the respective spots makes it possible to obtain a push-pull signalor a phase difference signal. Therefore, this makes it possible tosubject the tracking error signal to an optimal method selected fromamong the three-beam method, the push-pull method, and the phasedifference method according to the type of the information recordingmedium 3 used.

[0049] Furthermore, as shown in FIG. 9, which is an enlarged plan viewspecifically illustrating the photodetector element, the detectingportions 48 a, 48 b, 48 c, and 48 d for detecting reproduction signalsmay be arranged at equal distances from the emission point. Thisconfiguration allows the first diffraction grating 69 to have the samegrating periodic interval at all the plurality of diffraction gratingregions 69 a, 69 b, 69 c, and 69 d composing the first diffractiongrating 69. Therefore, when the first diffraction grating is formed byetching or the like, variation in manufacture, such as variation ofdepth of the gratings, is minimized. Consequently, it is possible tomanufacture the same with stable properties.

[0050] It should be noted that in the optical information processingdevice of FIG. 1, the objective lens 4 may be fixed in the opticalsemiconductor device 1 so as to be actuated integrally. This by no meansleads to the impairment of optical characteristics, such as a decreasein the signal quantity, that tends to occur when the objective lens isactuated independently. Therefore, it is possible to obtain excellentreproduction signals and focus/tracking error signals.

[0051] The optical semiconductor device according to the presentinvention can be defined in a broader sense. For instance, a so-calledoptical pickup device in which the optical semiconductor device 1, theobjective lens 4, and a part of the control mechanisms are modularizedalso is categorized as the optical semiconductor device of the presentinvention. On the other hand, in the case where the semiconductorelement 11 is dealt with independently, it is called a semiconductorlaser device or a light-receiving device, which also is categorized in abroad sense as the optical semiconductor device of the presentinvention.

[0052] Furthermore, although the above-described embodiments show anexample in which an area of the detecting portions for detectingreproduction signals is reduced, this invention is also applicable to adetecting portion that is required to perform high-speed processing fora different reason.

[0053] Industrial Applicability

[0054] With the present invention, it is possible to reduce an area of areproduction-signal-detecting photodetector element in an opticalsemiconductor device. This makes it possible to provide an opticalinformation processing device that is capable of performing high-speedreproduction and obtaining reproduction signals with an excellent SINratio.

1. An optical semiconductor device comprising: a laser element; anemitted beam dividing portion for dividing an emitted light beam fromthe laser element into a plurality of light beams; a reflected beamdividing portion for dividing a reflected light beam from an informationrecording medium into light beams in different focused states;servo-signal-detecting photodetector elements for receiving thereflected light beams obtained by the division by the reflected beamdividing portion in a defocused state; a first diffraction grating thatis provided in the emitted beam dividing portion and that diffracts thereflected light beam having passed through the reflected beam dividingportion; and a signal-detecting photodetector element for receivingreflected light beams having been subjected to the diffraction by thefirst diffraction grating.
 2. The optical semiconductor device accordingto claim 1, wherein the reflected light beam from the informationrecording medium that is diffracted by the first diffraction gratingsubstantially focuses on a surface of the signal-detecting photodetectorelement.
 3. The optical semiconductor device according to claim 1,wherein two diffracted light beams of the same order diffraction by thefirst diffraction grating are subjected to the diffraction withdifferent diffraction efficiencies, and the diffracted light beam havingthe higher diffraction efficiency is received by the signal-detectingphotodetector element.
 4. The optical semiconductor device according toclaim 3, wherein each grating in the first diffraction grating is of aninclined type having a step-like cross-sectional shape or a triangularcross-sectional shape.
 5. The optical semiconductor device according toclaim 1 or 2, wherein the first diffraction grating is composed ofgratings, each of which is in a curved line form.
 6. The opticalsemiconductor device according to claim 1 or 2, wherein the firstdiffraction grating is composed of a plurality of diffraction gratingregions having the same diffraction efficiency.
 7. The opticalsemiconductor device according to claim 1 or 2, wherein the firstdiffraction grating is composed of at least two diffraction gratingregions that differ from each other in a direction in which gratings arearranged.
 8. The optical semiconductor device according to claim 1 or 2,wherein the first diffraction grating is composed of diffraction gratingregions having the same grating periodic interval.
 9. The opticalsemiconductor device according to claim 1 or 2, wherein the firstdiffraction grating is composed of a plurality of diffraction gratingregions that divide a spot of the reflected light beam equally. 10.(cancelled)
 11. The optical semiconductor device according to claim 1,wherein: when the emitted beam dividing portion is positioned on anoptical axis extending between an emission point of the laser elementand a main spot formed via an objective lens on the informationrecording medium, the reflected light beam from the foregoinginformation recording medium entering a region satisfying a formulashown below is divided so as to be collected on the signal-detectingphotodetector element: r≦d 9×tan(sin⁻¹(NA)) where: d represents anair-equivalent distance from the emission point of the laser element tothe emitted beam dividing portion; NA represents a numerical aperture ofthe objective lens; and r represents a distance from a point at whichthe optical axis and the emitted beam dividing portion cross each otheron the emitted beam dividing portion.
 12. An optical element comprising:a first optical element that is provided on one surface of a transparentmember and that includes first and second diffraction gratings; and asecond optical element that is provided on the other surface of thetransparent member and that divides a reflected light beam into lightbeams in different focused states, wherein the first and seconddiffraction gratings are juxtaposed in a first direction, and gratingsof the first diffraction grating are arranged in a direction differentfrom the first direction.
 13. The optical element according to claim 12,wherein the first diffraction grating is of an inclined type having astep-like cross-sectional shape or a triangular cross-sectional shape.14. The optical element according to claim 12, wherein the firstdiffraction grating is composed of gratings each of which is in a curvedline form.
 15. The optical element according to claim 12, wherein thefirst diffraction grating is composed of at least two diffractiongrating regions that differ from each other in a direction in whichgratings are arranged. 16.(amended) An optical information processingdevice comprising: a laser element; an emitted beam dividing portion fordividing an emitted light beam from the laser element into a pluralityof light beams; an optical system for guiding the light beams obtainedby the division by the emitted beam dividing portion to an informationrecording medium; a reflected beam dividing portion for dividing areflected light beam from the information recording medium into lightbeams in different focused states; servo-signal-detecting photodetectorelements for receiving the reflected light beams obtained by thedivision by the reflected beam dividing portion in a defocused state; afirst diffraction grating that is provided in the emitted beam dividingportion and that diffracts the reflected light beam having passedthrough the reflected beam dividing portion; and a signal-detectingphotodetector element for receiving reflected light beams having beensubjected to the diffraction by the first diffraction grating.
 17. Theoptical information processing device according to claim 16, wherein thesignal-detecting photodetector element has a light-receiving areasmaller than a light-receiving area of the servo-signal-detectingphotodetector elements.
 18. The optical semiconductor device accordingto claim 1, wherein: a pair of the servo-signal-detecting photodetectorelements are arranged symmetrically with respect to an optical axis; andthe signal-detecting photodetector element is arranged at a shorterdistance from the optical axis than the servo-signal-detectingphotodetector elements and has a light-receiving area smaller than alight-receiving area of the servo-signal-detecting photodetectorelements, wherein the pair of the servo-signal-detecting photodetectorelements and the signal-detecting photodetector element are integrated.19. The optical semiconductor device according to claim 18, wherein thesignal-detecting photodetector element is positioned closer to one ofthe servo-signal-detecting photodetector elements.
 20. The opticalsemiconductor device according to claim 18, wherein the signal-detectingphotodetector element is provided in substantially a same plane as theemission point.
 21. The optical semiconductor device according to claim18, wherein the signal-detecting photodetector element is divided into aplurality of detecting sections having substantially equal areas.